Sliding material comprising fluorine plastic and binder resin

ABSTRACT

The sliding properties of a sliding material which comprises fluorine-plastic and binder resin are improved, such that it withstands high speed and high load and varying sliding conditions from the lubricating-oil free condition to the lubricating-oil condition and vice versa. A novel sliding material comprises fluorine-plastic particles having a flat ratio of from 1.5 to 10 in terms of an average aspect ratio and binder resin.

FIELD OF INVENTION

The present invention relates to sliding material, particularly slidingmaterial comprising fluorine plastic and binder resin for bonding thefluorine plastic, more particularly, the sliding material, which issuited for depositing on the sliding surface of a swash plate of theswash-plate compressor.

BACKGROUND OF INVENTION

Fluorine plastic exhibits excellent low-friction property under the drylubricating condition. However, in order to improve the wear resistanceof the fluorine plastic-based sliding member, the fluorine plastic isblended with a solid lubricant such as MoS₂, graphite and the like andthey are bonded with base resin.

In the prior art, in order to improve the sliding properties of thefluorine-plastic based sliding material, the proportion ratio or amount,and the particle diameter of the additives, have been adjusted.

For example, it is disclosed in Japanese Unexamined Patent PublicationNo. 7-97517 that a sliding material, which consists of from 50 to 73% byweight of at least one of polyamide resin and polyimide resin, from 3 to15% by weight of polytetrafluoroethylene (PTFE) resin as solidlubricant, from 20 to 30% of molybdenum disulfide (MoS₂) and from 2 to8% by weight of graphite, exhibits improved wear resistance and initialcompatibility under the conditions of lubrication by graphite containedin the gray cast iron, low sliding speed of from 0.08 to 1 m/second, andrelatively low load. This material is appropriate for use as the surfacelayer of a piston skirt.

It is disclosed in Japanese Unexamined Patent Publication No.2000-136397 that sliding material, which contains from 10 to 40% byweight of calcined granular PTFE and from 3 to 40% by weight ofgraphite, the balance being a binder resin, i.e., polyimide and/orpolyamide imide, exhibits improved sliding properties under the drycondition, and is appropriate as the sliding material of a wiper arm,which is operated under a low speed of 20 mm/s and relatively low load.The granular calcined PTFE is prepared by means of forming PTFE powderby suspension polymerization or emulsion polymerization, heating theresultant PTFE powder to melting temperature, i.e., calcining, and thenpulverizing the calcined PTFE powder.

A swash-plate type compressor, an example of which is shown in FIG. 1,comprises the following members: cylinder block 1; valve plates 2;cylinder heads 3; a driving shaft 4; thrust bearings 5; radial bearings6; a mechanical seal 7; a swash plate 8; a swash-plate chamber 10, inwhich the swash plate 8 is mounted; a cylinder bore 11; a piston 12;balls 13; ports 15 formed through the valve plates 2; and ejectingchambers 16; ports (not shown) communicated with the ejectingchambers16; the ejecting chambers (not shown); and suction chambers 21.In such swash-plate type compressor, the driving shaft 4 is rotarydriven so as to rotate the swash plate 8 which is integral with thedriving shaft 4. Along with the rotation of the swash plate 8, thepiston 12 is reciprocated, thereby compressing cooling media within thecylinder bore 11. The compressed cooling media are ejected into therespective ejection chambers 16A, 16B via the ports 15A, 15B,respectively. The compressed cooling media is then sucked into thecylinder bore 11 via the ports 17, the ejection ports 19, ports 20, apair of the suction chambers 21A, 21B, not-shown sucking valves, andports 15A formed through the valve plate 2A. The lubricating oilcontained in the compressed cooling media is introduced into theswash-plate chamber 10 under a mist condition and is fed to the slidingportions of the swash plate 8, the thrust bearings 5 and the like.

The prior art related to the surface treatment of a swash plate of theswash-plate type compressor includes the following.

-   -   (1) European Patent No. 713972B1. The Cu or Al alloy is        flame-sprayed, and if necessary, the Pb or Sn coating is, then,        plated on the flame-sprayed layer.    -   (2) U.S. Pat. No. 6,123,009. The flame-sprayed Cu layer is        coated with MoS₂ or PTFE coating film.    -   (3) Japanese Unexamined Patent Publication No. 02-002475. A        solid-lubricant layer is formed on the aluminum-alloy substrate.    -   (4) Japanese Unexamined Patent Publication No. 2000-265953.        Metallic particles are incorporated in the resin layer.    -   (5) Japanese Unexamined Patent Publication No. 2002-005013.        Amorphous hard carbon (DLC) film is formed on the swash plate.    -   (6) Japanese Unexamined Patent Publication No. 2002-036902.

A coating film consisting of a mixture of a solid lubricant and PEEKresin is formed on the swash plate.

-   -   (7) Japanese Unexamined Patent Publication No. 2002-89437 A        coating film consisting of a mixture of solid lubricant and        earthy graphite resin is formed on the swash plate.    -   (8) Japanese Unexamined Patent Publication No. 2002-180961. A        resin coating or a plating layer is deposited on the surface of        a sintered layer.

The PTFE contained in the coating composition according to the prior art(2) mentioned above exhibits a low-friction effect at the sliding withshoes, under such a lubricating-oil poor sliding condition that aswash-plate type compressor mounted in a vehicle is started and drivento rotate and is lubricated only by the cooling media. Specifically,heat generation is suppressed by PTFE. On the other hand, when it isdesired to rapidly cool the interior of a vehicle, the swash-plate typecompressor is operated under the sliding conditions of high speed andhigh load. In this case, the PTFE contained in the coating compositionundergoes serious peeling wear so that the surface is drasticallydamaged and seizure occurs.

The surface treatment according to the prior art (1) mentioned aboveprovides the coating film consisting only of metal. There is apossibility that the swash plate subjected to this surface treatment mayseize with respect to the opposite member, i.e., the shoes, under poorlubricating-oil operating conditions.

The surface treatments according the prior arts (3), (4), (6), and (7)mentioned above provide a solid-lubricant coating film on the surface ofmetal. This coating film may incur under such recent sliding conditionsas high-speed rotation and high load a problem of peeling.

The surface coating of DLC according to the prior art (5) mentionedabove may crack under the reciprocating load like the case of resincoating film.

The prior art (8) mentioned above provides a resin coating layer or aplating layer on the sintered metallic layer. Since the contact areabetween the resin coating layer and the sintered metal is larger thanthat of such layer and the non-sintered and hence non-porous metal,peeling of the resin coating layer is impaired. However, fundamentally,the peeling of the resin coating cannot be prevented, because the resinis of low strength and cannot withstand the load from the shoes.

SUMMARY OF INVENTION

It is, therefore, an object of the present invention to improve thesliding properties of a sliding material which is subjected to highspeed and high load and is used under varying sliding conditions fromthe lubricating-oil free condition to the lubricating-oil condition andvice versa.

It is a particular object of the present invention to lessen the peelingwear of the sliding material containing PTFE and to modify its wearmechanism such that little wear occurs gradually and hence an improvedcompatible surface is formed.

In accordance the objects of the present invention, there is provided asliding material, which comprises fluorine-plastic particles having aflat ratio of from 1.5 to 10 in terms of the average aspect ratio andbinder resin.

There is also provided a sliding material, which comprisesfluorine-plastic particles having a flat ratio of from 1.5 to 10 interms of the average aspect ratio and binder resin.

The fluorine plastic particle is preferably at least one selected fromthe group consisting of polytetrafluoroethylen (PTFE),tetrafluoroethylene perfluoroalkoxy vinyl ether copolymer(PFA),perfluoroethylene propylene tetrafluoroethylenen hexafluoropylene(FEP),ethylene-tetrafluoroethylene copolymer (ETFE), polyvinyldenefluoride(PVdF), and ethylene-chlorotrifluoroethylene copolymer (ECTFE).

In the description hereinafter, the fluorine plastic is described byreferring to a representative example of PTFE.

The granular PTFE particles have smaller surface area than the flat PTFEparticles. The bonding strength of the former particles with the binderis, therefore, lower than that of the latter particles. The formerparticles are, therefore, liable to separate from the binder, so thatpeeling of PTFE is induced. Contrary to this, the sliding materialcomprising the flat PTFE particles bonded with the binder has improvedcompatibility such that fluid lubrication can be realized on the surfaceof the sliding material.

Meanwhile, under such poor oil condition at the initial sliding periodthat only the cooling media lubricates, PTFE exhibits low-frictionproperty independently upon the shape of PTFE particles. The frictionbetween the PTFE-containing sliding material and a shoe is, thereforelow during sliding. Specifically, the extremely thin surface of the PTFEparticles having a thickness of few atom-layers is subject to cleavage.This process takes place even under extremely weak external force, sothat satisfactorily low friction is realized.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional drawing of a swash-plate type compressoraccording to an example.

FIG. 2 is a graph showing a relationship between the average aspectratio of the PTFE particles and the seizure time of the PTFE basedsliding material. The average aspect ratio in a range of from 1 to 5 isshown in a larger scale than that of from 5 to 10 and 10 to 15.

FIG. 3 is a schematic drawing of a sliding layer, which contains flatPTFE, graphite and MoS₂.

DESCRIPTION OF PREFERRED EMBODIMENTS

The granular PTFE particles can be flattened by means of impartingstrong shear blending. A bead mill blender, which can perform strongshear blending, was used to prepare the solid-lubricant coating-mixture,which may be referred to as the paint. The average aspect ratio of PTFEparticles and the blending time of the paint were investigated. Theseizure time in dependent on the average aspect ratio was alsoinvestigated.

The composition of the paint was 60% by volume of PAI, 20% by volume ofPTFE, and 20% by volume of graphite for every blended mixture with thevaried average aspect ratio.

The testing condition was as follows.

Testing Machine: 3 pin/disc type seizure tester

Load: 1.2 kN

Number of Revolutions: 1000 rpm

Lubricating Condition: R 134 gas

Opposite Shaft: SUJ 2 (shoe form)

As is clear from FIG. 2, the seizure time increases with increase in theaverage aspect ratio up to approximately 0.2. The seizure time thendecreases because the strength of PTFE decreases excessively due toflattening. Based on this result, the average aspect ratio of the PTFEparticles is limited in a range of from 1.5 to 10 according to thepresent invention. A preferable average aspect ratio is from 2 to 5. ThePTFE particles present on a surface area of 1 mm×20 μm were measured interms of the ratio of long diameter/short diameter, and the averagevalue of the measured values was calculated as the average aspect ratio.

The binder is selected from a heat-resistant resin and is preferably atleast one selected from polyamide imide and polyimide. Proportion of thefluorine plastic particles is preferably from 5 to 40% by volume, morepreferably from 15 to 35% by volume based on the total volume of thefluorine plastic particles and binder, or the total volume of thefluorine plastic particles, the wear-resistant additives and/or thesolid lubricant, and the binder. Either of these volumes is hereinafterreferred to as the total volume.

If necessary, at least one solid lubricant selected from the groupconsisting of MoS₂ and graphite is contained in a proportion of from 2to 20% by volume based on the total volume. The balance is from 98 to80% by volume of the fluorine-plastic particles and the binder resin.

In addition, at least one wear resistant additive selected from thegroup consisting of SiO₂, TiO₂, SiC and Al₂O₃ may be contained in aproportion of from 0.1 to 5.0% by volume based on the total volume. Thebalance is from 99.9 to 95.0% by volume of the fluorine-plasticparticles and the binder resin.

When the paint is subjected to strong shear blending, the granular PTFEcontained is flattened in the paint. For example, the calcined fluorineplastic having from 2 to 20 μm of average particle diameter may beblended with the other starting materials within a bead mill developedby IPROS Corporation, and the sliding material according to the presentinvention may be thus prepared.

The sliding material according to the present invention can bepreferably used for, for example, the sliding layer of a swash-platetype compressor and the like, which is operated under high pressure andhigh speed and lubricating oil supplied on the sliding surface.

EXAMPLES

The paint having the blended composition shown in Tables 1 and 2 wassubjected to blending with a propeller mixing (Comparative Example,untreated PTFE) and blending with strong shear blending by means of abead mill (Examples, flattened PTFE).

The respective components were as follows.

-   -   PTFE: product of Kitamura Co., Ltd., KTL-8N    -   PAI: product of Hitachi Kasei Co., Ltd., HPC-6000    -   MoS₂: the average particle-diameter—25 μm; a product of Sumitomo        Mining Lubricant Co., Ltd, Molypowder PB    -   Graphite: the average particle-diameter—1 μm, a product of        Nippon Graphite Co., Ltd., CSSP

The prepared powder was applied on the substrate of a swash-plate toprovide a coating thickness of 20 μm, and the surface of the coating waspolished to form approximately 0.3 μm Rz of roughness.

The testing condition was under no lubrication of the lubricant oil andas follows.

-   -   Testing Machine: 3 pin/disc type seizure tester    -   Load: 1.2 kN (4 MPa)    -   Number of Revolutions: 1000 rpm (4.2 m/s)    -   Lubricating Condition: R 134 gas    -   Opposite Shaft: SUJ 2 (shoe form)

The test results are shown in Table 1. TABLE 1 Proportion of ResinComponents vol % Test Result PAI MoS₂ Gr PTFE Seizure Time (sec) Example55 20 15 10 140˜160 PTFE-Flattening 60 — 20 20 180 or more (AverageAspect Ratio-3) Comparative Example 55 20 15 10 120˜140 PTFE Untreated60 — 20 20 130˜160 (Average Aspect Ratio-1)

It is apparent from Table 1 that the inventive examples are superior tothe comparative examples in view of the seizure resistance.

The test conditions was under lubrication of lubricating oil and coolingmedia and were as follows.

-   -   Testing Machine: high-pressure environmental-gas friction tester    -   Lubrication: circulation type (ice-machine oil+chlorofluoorcaron        gas)    -   Load: 2 MPa/15 minutes, successive increase to 16 MPa at the        maximum    -   Number of Revolutions: 7200 rpm    -   Opposite Shaft: SUJ 2 (shoe form)

The test results are as follows. TABLE 2 Proportion of Resin Componentsvol % Test Result PAI MoS₂ Gr PTFE Seizure Wear Example 55 20 15 10 non3 μm PTFE-Flattening 60 — 20 20 non 8 μm (Average Aspect Ratio-3)Comparative Example 55 20 15 10 non 5 μm PTFE Untreated Slight (AverageAspect Peeling Ratio-1) 60 — 20 20 Seizure Peeling

It is apparent from Table 2 that no peeling occurs in the inventiveexamples.

As is described hereinabove, the present invention provides slidingmaterial with small wear and free of peeling, when used as the slidingmaterial on a swash plate of a swash-plate type compressor.

1. Sliding material, which comprises fluorine-plastic particles having aflat ratio of from 1.5 to 10 in terms of an average aspect ratio andbinder resin.
 2. Sliding material according to claim 1, wherein saidfluorine-plastic is at least one selected from the group consisting ofpolytetrafluoroethylen (PTFE), tetrafluoroethylene perfluoroalkoxy vinylether copolymer(PFA), perfluoroethylene propylene tetrafluoroethylenenhexafluoropylene(FEP), ethylene-tetrafluoroethylene copolymer (ETFE),polyvinyldenefluoride (PVdF), and ethylene-chlorotrifluoroethylenecopolymer (ECTFE).
 3. Sliding material according to claim 1, whereinsaid fluorine-plastic particles are the calcined fluorine plastic, whichhas from 2 to 20 μm of average particle diameter and which is thencrushed.
 4. Sliding material according to claim 1, wherein said binderresin is at least one selected from the group consisting of polyamideimide and polyimide.
 5. Sliding material according to claim 2 consistingof from 5 to 40% by volume of said fluorine plastic particles and from95 to 60% by volume of said resin binder in balance.
 6. Sliding materialaccording to claim 1, further comprising from 2 to 40% by volume of asolid lubricant selected from the group consisting of MoS₂ and graphite,the balance being said fluorine-plastic particles and said binder resinin an amount of from 98 to 60% by volume.
 7. Sliding material accordingto claim 1, further comprising from 0.1 to 5.0% by volume of awear-resistant additive selected from the group consisting of SiO₂,TiO₂, SiC and Al₂O₃, the balance being said fluorine-plastic particlesand said binder resin in an amount of from 99.1 to 95.0% by volume. 8.Sliding material according to claim 1, further comprising from 2 to 40%by volume of a solid lubricant, and from 0.1 to 5.0% by volume of awear-resistant additive selected from the group consisting of SiO₂,TiO₂, SiC and Al₂O₃, the balance being said fluorine plastic and saidbinder resin.
 9. Sliding material according to claim 1, deposited on asliding portion of a swash plate of a swash-plate type compressor.